The invention relates to a method and an apparatus for contactless roll gap measurement and control with the aid of light beams.
Hitherto the roll gap has been determined only indirectly with the aid of measuring means which were attached to the mountings, e.g. the support rollers. The values were corrected in accordance with the frame springing of the roll stand which could be determined from the measurement of the rolling pressure by strain gages. The determination of the roll gap by this method was inaccurate.
Hitherto a direct and more accurate measurement at the roll gap was not possible in particular in hot-rolling mills due to the high temperature and the dirt.
German patent application No. 2,404,763 discloses a measuring device which measures the gap between the necks or journals of the working rolls and which can be pivoted out of the gap to enable the rolls to be changed without obstruction. In accordance with the electromagnetical measuring system of German patent application No. 2,404,763 the roll gap can be determined only in cold-rolling mills with adequate accuracy because the device is greatly influenced by temperature fluctuations caused for example by glowing rolled material in hot-rolling mills. A further disadvantage of this known device resides in that its measurement range is only very small. It thus cannot be used in reversible stands as are usual in roughing rolling trains in hot-rolling mills.
In such roughing rolling trains the setting of the rolling gap changes for example within 80 sec. 3 times, the rolling gap varying in magnitude for example from 125 mm to 60 mm.
It is the problem underlying the present invention to provide a measuring method and an apparatus with which extremely accurate and reliable determinations of the rolling gap are possible even in roughing or cogging trains for hot-rolling mills with a very large measuring range.